Electric power steering apparatus

Abstract

An electric power steering apparatus includes a speed reducing mechanism for decelerating the rotation of a rotatable shaft in an electric motor and a converting mechanism for converting the output rotation of the speed reducing mechanism into the axial movement of a steering shaft extending toward the right and left sides of a vehicle. The speed reducing mechanism includes an input pulley driven by the electric motor, an output pulley arranged with the steering shaft enclosed thereby, a belt for connecting the input pulley and the output pulley to each other, and a belt tension adjuster.

1. An electric power steering apparatus comprising an electric motor for producing a steering assist force, further comprising:
 a speed reducing mechanism for decelerating a rotation of a rotatable shaft in the electric motor; and  
 a converting mechanism for converting an output rotation of the speed reducing mechanism into an axial movement of a steering shaft extending toward right and left sides of a vehicle,  
 the speed reducing mechanism comprising  
 an input pulley driven by the electric motor,  
 an output pulley arranged with the steering shaft enclosed thereby,  
 a belt for connecting the input pulley and the output pulley, and  
 means for adjusting a tension of the belt; wherein  
 the means for adjusting the tension includes means for changing a center-to-center distance between the input pulley and the output pulley; wherein  
 the means for changing the center-to-center distance includes a guiding mechanism for relatively guiding the first housing for holding the input pulley and the second housing for holding the steering shaft in a predetermined guiding direction in which the center-to-center distance can be changed; and wherein  
 the predetermined guiding direction includes a direction perpendicular to a plane including center lines of the input pulley and the output pulley.  
 
   
   
     2. The electric power steering apparatus according to  claim 1 , wherein
 the predetermined guiding direction includes a direction perpendicular to the center lines of the input pulley and the output pulley.  
 
   
   
     3. The electric power steering apparatus according to  claim 1 , wherein
 the guiding mechanism includes a guiding mechanism having a screw for connecting the opposite portions of the first housing for holding the input pulley and the second housing for holding the steering shaft and a screw insertion hole composed of a slot provided in one of the opposite portions and extending in the predetermined guiding direction.  
 
   
   
     4. The electric power steering apparatus according to  claim 1 , wherein
 the means for changing the center-to-center distance further comprises a screw which can relatively drive the first and second housings in the predetermined guiding direction.  
 
   
   
     5. The electric power steering apparatus according to  claim 1 , wherein
 the means for changing the center-to-center distance further comprises an elastic member for relatively urging the first and second housings in the predetermined guiding direction.  
 
   
   
     6. The electric power steering apparatus according to  claim 1 , wherein
 the means for adjusting the tension includes a tensioner having a fixed member, a movable member, a tensioner pulley supported on the movable member so as to be rotatable and engaging with the belt, and urging means for urging the tensioner pulley through the movable member in the direction in which tension is applied to the belt.  
 
   
   
     7. The electric power steering apparatus according to  claim 6 , wherein
 a slack side of the belt is pressed toward a tension side by the tensioner pulley so that a belt wrap contact area on the input pulley expands.  
 
   
   
     8. The electric power steering apparatus according to  claim 7 , wherein
 a pitch circle diameter of the input pulley is within a range of 12 to 30 mm, and  
 a center angle of the input pulley, corresponding to the belt wrap contact area on the input pulley, is within a range of 135 to 210 degrees.  
 
   
   
     9. The electric power steering apparatus according to  claim 1 , wherein
 the belt comprises a cocked belt, and  
 the input pulley and the output pulley respectively comprise a toothed pulley.